The invention relates to ink jet recording apparatuses. More particularly, it is directed to an ink jet recording apparatus capable of forming high-quality images even on hydrophobic or less hydrophilic recording media, such as light-transmitting recording media used for originals of overhead projectors (OHP).
A variety of ink jet recording apparatuses that make a recording by jetting ink droplets on a recording medium have heretofore been developed. Among them is a color ink jet recording apparatus that has a plurality of heads and jets a plurality of color inks from such heads to produce color images.
Along with the development of recording apparatuses grows a demand for diversification of recording media to be used therefor. In addition to conventionally used printing paper that is highly hydrophilic, paper such as light-transmitting recording media for use in OHP originals should also be included. In this case, hydrophobic light-transmitting recording media having been subjected to such a treatment by which the media can accept ink will be used.
It is high speed recording that must be achieved by recording apparatuses. As the recording speed of the ink jet recording apparatuses is increased, improper superposition or misalignment of dots is caused and thus their recording quality becomes impaired. To overcome this shortcoming, the conventional ink jet recording apparatuses record at such a highest possible speed as can confine the improper superposition or misalignment to a degree not objectionable to users.
The users are not aware of the improper superposition or misalignment of dots caused by a recording at such recording speed when a normal recording medium is used. However, such defect becomes distinct when a hydrophobic light-transmitting recording medium is used.
To overcome this problem, a recording apparatus is disclosed in, e.g., Japanese Patent Unexamined Publication No. 312155/1988. This recording apparatus scans twice to form dots on a light-transmitting recording medium by overlapping one dot upon another or by filling up the space between dots. As a result of this method, a high-density image free from blots can be produced.
Also proposed in Japanese Patent Unexamined Publication No. 4523/1990 is a recording apparatus that repeats the printing of a single line of data per color as many as a number of colors to be used to make a single line of multi-color recording. As a result of this method, blots in printed dots can be reduced.
These conventional recording apparatuses require a plurality of rounds of scanning to print a single line of data. This is not only time-consuming but also impairs printing quality due to improper superposition of dots caused during the plurality of rounds of scanning.
FIGS. 3 (A) to (D) are diagrams illustrative of prints produced by the conventional recording methods. FIG. 3 (A) shows arrays of dots printed by a first round of scanning; FIG. 3 (B) shows arrays of dots at the time of superposing a plurality of colors by first and second rounds of scanning; FIG. 3 (C) is a horizontal sectional view of FIG. 2 (B); and FIG. 3 (D) shows an array of dots at the time of printing a thin line. The printing method involving a plurality of rounds of scanning is liable to cause improper superposition of dots as shown in FIG. 3 (B). When the dots are printed while improperly superposed, the section of such printing exhibits, as shown in FIG. 3 (C), incomplete superposition of colors, thus causing color unmatching in the direction in which the dots are improperly superposed. In the case of printing thin lines, high-speed printing tends to cause turbulence in jetting ink. Less hydrophilic recording media such as hydrophobic light-transmitting recording media is liable to misalignment of dots, which results in inconsistent image quality such as shown in FIG. 3 (D).